Just be careful putting "traps" up. If someone was injured then they could get u in alot of trouble with the law. Its stupid how stuff like that works. On my parents farm, we have to take down our electric fence that goes across our creek every winter, cause apparently if a snowmobiler hits the fence (even though they dont have permission to be there) we can be charged.
Our flying field had similar problems with off roaders. we posted a few signs, and put up fencing around the parking area (had to for insurance purposes) and it cut down alot of it. I guess if someone is always stopping in (a pain to do, but it works) they will realize that someone might see them, and they will find another place to tear up.